Wikipedia:Reference desk/Archives/Science/2009 December 15

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

December 15

Why isn't t-butyl (as a carboxylate protecting group) sensitive to base?

It seems to me you could perform an E2 elimination and kick out carboxylate as a decent leaving group .... John Riemann Soong (talk) 00:24, 15 December 2009 (UTC)

The point of using a t-butyl protecting group is that the t-butyl structure represents an extremely bulky group, so effectively the bulk of this group shields the central carbon atom from attack by a base, therefore any elimination requires significantly higher energy than other smaller groups. Rjwilmsi 23:06, 15 December 2009 (UTC)

That sounds like a conflation of SN2 and E2 modes of reaction. To answer the original question, I ponder "carboxylate as a decent leaving group". They are easily ejectable if you can generate a β anion directly (2-haloethyl esters under reducing conditions), but I don't know if carboxyl is able to activate β H for direct deprotonation effectively (E2). Are ethyl esters noticeably less stable to non-nucleophilic bases (compare steric shielding of the β H)? DMacks (talk) 23:14, 15 December 2009 (UTC)

Boiling water simply by adding kinetic energy?

Is it possible in principle to bring water from room temperature to a boil simply by adding kinetic energy via something like an egg beater? If yes, is it possible given the tools available in the average home, or would you need some serious manufacturing/industrial class hardware? Just curious as I gently stir my morning coffee... 218.25.32.210 (talk) 00:40, 15 December 2009 (UTC)

In theory yes, but it'd be very impractical. A major problem is heat dissipation. (At some point the water will lose more heat than you are adding to it.) And efficiency. An egg-beater is way too weak ... a major problem is that you'll just end up heating the room air instead. If you completely insulated the boiling apparatus in question, and ensured very little heat flow between the container and the outside environment, and dropped in an agitator, you could prolly theoretically boil it. The heat capacity of water (or any solvent for that matter -- even hexane) is kinda large though. John Riemann Soong (talk) 00:46, 15 December 2009 (UTC)

Given the right circumstances - certainly. If you take an electric drill with a really blunt wood-bit - and try to drill your way into a small chunk of stainless steel - after a couple of minutes of fruitless drilling, squirt a small amount of water into the area and it'll boil immediately. Now, admittedly - we took the kinetic energy of the drill - and used friction to convert that to heat - but the intermediate step is merely a convenience. The question is really whether you can figure out a way to get from motion to convert directly into heat in the liquid. In principle, it's certainly possible - and with a sensitive enough thermometer you'd certainly be able to measure a small, slow heat increase from a fast electric mixing machine or such like. But as John said - the problem is to get the heat into the liquid faster than it'll lose heat to the environment. So you need to agitate the water as fast as possible to get the heat in faster than it's losing it. You'd want an insulated container...that kind of thing. It's got to be possible though - it's just a matter of figuring out a way to do the experiment. SteveBaker (talk) 01:31, 15 December 2009 (UTC)

My favourite candidate so far is to use a magnetic stirbar. No moving parts, and you could theoretically seal up the container with lots of insulation, then just apply a changing magnetic field! =D Better yet, drop fine magnetic powder and turn on the field. The big thing you see is surface area. If you do some simple calculations, you find your agitator is adding very little energy (most of the energy doesn't end up in the water, even without the water losing anything). Very fine particles being moved about means more surface area ===> more friction ===> greater heating efficiency. John Riemann Soong (talk) 01:36, 15 December 2009 (UTC)

Nod, keep in mind that 'heat energy' is for all intents and purposes just kinetic energy on a small scale, IE the energetic movements of atoms unless I was deceived as a child. Unomi (talk) 01:44, 15 December 2009 (UTC)

An interesting extension is to use something with an electric dipole or that is ionic...apply an oscillating electric field and the molecules vibrate and collide with each other to heat the material. 173.79.45.179 (talk) 05:17, 15 December 2009 (UTC)

Related: frictional heating from the mixing is an important factor when kneading bread dough mechanically. --Sean —Preceding unsigned comment added by 76.182.94.172 (talk) 01:34, 15 December 2009 (UTC)

I've been told that a step in the commissioning of a nuclear power plant is to generate steam and produce a few megawatts of power from the turbogenerator without any nuclear power input, simply by running the boiler feed pumps to recirculate the water in the boiler. James Prescott Joule investigated the mechanical equivalent of heat in the mid 1800's. He used a falling weight to spin a paddle in an insulated container of water, and noted how much mechanical work it took to raise a given mass of water by a given temperature.His result was 772.24 foot pound force (4.1550 J·cal-1). He found that 772.24 foot-pounds of work raised one pound of water 1 degree F. His claims were rejected by many scientists, who still like "caloric" theories and did not generally accept conservation of energy as part of their core scientific beliefs, but eventually gained acceptance. See also Mechanical equivalent of heat. I leave as an exercise for the reader how much work one would have to do to raise say 1 liter of water from 20 c to 100 c by manually spinning the paddles, or cranking an eggbeater in an insulated bit of water. If a healthy person can produce 1/4 horsepower for over an hour, where a horsepower is 746 watts or 33000 pound-feet per minute how long would it take at 100% efficiency in the mechanical apparatus and perfect insulation of the water container to get a liter of water boiling? (Today we know that the question basically "boils down" to Joules per second of energy input and the specific heat of water.) Edison (talk) 15:37, 15 December 2009 (UTC)

Actually this is one case I think where the apparatus would not need to be 100% efficient, since losses in efficiency are caused by things like friction, which would generate that heat anyways. 65.121.141.34 (talk) 16:35, 15 December 2009 (UTC)

I was assuming no friction outside the insulated water vessel, like in a treadmill linkage , or pulleys to speed up the rotation, or a gear box, and all. Note that .25 horsepower as the human input is also a crude number, so it could be .1 hp or .5 hp for a few minutes, and depends on the fitness of the individual. So would it take seconds, minutes, hours, or days for a hard working person to boil 1 insulated liter of water by mechanical agitation? Edison (talk) 00:40, 16 December 2009 (UTC)

So with the above caveats, and Joule's figures of 772.24 foot-poundforce of work required to raise one pound of water 1 degree F, an assumed 1/4 horsepower of human effort (8250 foot-poundforce per minute), starting at 70 deg F, neglecting changes in specific heat of water, 2.2 pounds of water per kg, I get 29.2 minutes of hard work to raise it to 212 °F (100 °C). At a more relaxed 1/10 horsepower (74.6 watts human effort), it would take 73.1 minutes. This only raises the water to the boiling point, but does not boil it away. It is interesting that in 1842, when Joule presented his findings, conservation of energy was in doubt among scientists. It took Joule and Helmholtz to lay the groundwork for modern physics, chemistry and engineering in this area. Joule's work was initially denied publication because they saw him as a non-scientist, and they doubted he could accurately measure very small temperature changes. Edison (talk) 20:12, 16 December 2009 (UTC)

Car windows again

The above question from yesterday reminds me of a related question that I have long puzzled over. Several people have assured me that setting the blowers to cold will clear condensation from the inside of a windscreen quicker than if they were set to warm. This does seem to be true, even though it goes against what I would intuit: shouldn't warm air perform this function more efficiently?--Shantavira|^{feed me} 08:25, 15 December 2009 (UTC)

The condensation is there because the car is warm inside while it's cold outside. So why do warm blowers work at all? 213.122.69.70 (talk) 08:50, 15 December 2009 (UTC)

Did you even bother to read the answers from yesterday? Warm blowers work because the problem is cold windows in wet air. If you warm up the windows (by blowing warm air on them), the condensation will get slower and slower until it stops, and in addition, the warm air will evaporate the drops that are already there, because warm air can "store" more water vapor than cold air (and the flow of air helps, too). --TheMaster17 (talk) 09:19, 15 December 2009 (UTC)

I read the sentence about the dew point, yes, but I didn't know car blowers preferentially heat the windows. The ones I'm familiar with are pointed towards the middle of the car. I didn't know that warm air can store more water vapour than cold air, either - does that reduce the effective humidity, meaning the dew point gets lower? I guess that's the critical piece of information. 81.131.54.224 (talk) 15:24, 16 December 2009 (UTC)

You may be misunderstanding the advice... if you turn on the air conditioning, it will dry the air and improve evaporation. But even with the air conditioning on, you should have the heater set to warm, so the air that blows is warm and dry. -- Coneslayer (talk) 12:31, 15 December 2009 (UTC)

There are two effects going on here. The amount of water that the air can hold depends on temperature. Warm air can hold lots of water - cold air, much less. So - when your car is cold, the water in the warm air in your breath hits the cold windshield and cools rapidly. At that point, the water can't stay in the air so it forms as droplets on the windshield. Hence:

• The A/C cools the air - but also dries it (it's not an "air refrigerator" - it's an "air conditioner" - it "conditions" the air - removing dust and moisture as well as cooling it down). Drying the air reduces the water content (irrespective of temperature) and without water in the air, there is nothing to condense.
• The heater warms up all of the air in the car - but since that air was formerly cold - it didn't have much water in it. So now the car is warm (and dry) and your breath can dissipate water into all of the other warm air in the car which (being dry) is easily able to hold it. Also, the warm air heats up the windshield so that when warm, moist air does touch it, it's not cooling the air down enough to allow the water to condense.

Hence either heating or cooling the car will eliminate mist from the glass. In fact, because the main source of all of this water is your body - simply turning on the fan and replacing the air inside the car with outside air will remove much of the moisture and prevent misting. Just blowing the air onto the windshield will maintain a barrier of drier air and thereby prevent your moist breath from getting in contact with it.

Hence, almost anything you do with the car's heating/cooling controls will help to demist it. However, the airconditioner (on cold) works best because it's literally removing the water - not just moving it around. SteveBaker (talk) 14:44, 15 December 2009 (UTC)

". . . The main source of all of this water is your body . . . ." Steve, you've been living in Texas for too long :-)! Back here in waterlogged Ukland, the environmental humidity (combined with lack of sunlight) is the principal problem - my internal fogging accumulates during the days I haven't driven, not when I'm in the car and driving - and hence delays my starting out. 87.81.230.195 (talk) 15:30, 15 December 2009 (UTC)

I disagree - on a cold day, there simply isn't "room" in the air for much water. Even at 100% humidity, there isn't much water in cold air. But the air from your lungs has been warmed and moisturized...so it does add the majority of the water. Your car may fog up when it's warmer inside the car than out - but there has to be some other source of water...perhaps you have a water leak accumulating water in the upholstery or carpet. If so - you need to fix it before you get mold growing in there - it's virtually impossible to erase the stink of mold in a car. SteveBaker (talk) 18:14, 15 December 2009 (UTC)

Fair point. I'll look for a leak as far as I'm able. 87.81.230.195 (talk) 10:34, 16 December 2009 (UTC)

Shatika

Resolved

Where can I find more information on Shatika? Regards-Shahab (talk) 09:07, 15 December 2009 (UTC)

Irrelevant discussion because OP mis-spelled sciatica

My guess would be that the snake oil article would be a good place to start. Keep in mind that these sorts of products are rarely regulated, so their claims of efficacy may be totally fictional. Nimur (talk) 13:16, 15 December 2009 (UTC)

Don't be too hard here. The product is Ayurvedic rather than allopathic. Sometimes I think we're guilty of judging one culture by another culture's lights. I know that's heresy on a science reference desk, but what the hey. --TammyMoet (talk) 13:51, 15 December 2009 (UTC)

Oh - yes, we can be that hard! This is the science desk and we don't stick our heads in the sand and say things are OK just because it comes from another culture and therefore we must respect it somehow. That is 100% not how science works - we judge things by the facts - and culture simply doesn't enter into the equation. What you just said is beyond heresy - it's completely f**king stupid.

So - let's do this properly. Let's examine the claims made for the stuff: It says that it "Relieves pain" - OK - maybe. Much of pain is psychosomatic and any placebo can do that. So - yeah - maybe.

But it also says that it cures: Arthritis(Osteoarthritis,rhumetoid arthritis),Spondylitis and Migraine. Pick any one of those: Osteoarthritis let's say. This is a disease that's caused by physical wearing and degradation of cartilage around the joints. Unless this oil somehow causes a magical regeneration of cartilage (something completely unknown in humans) - then it can't "cure" osteoarthritis - at best it might relieve the pain - but they already said it relieves pain in general, so they must be talking about something more specific. We don't say "Tylanol cures Osteoarthritis" - although it does help the pain. Spondylitis isn't even a specific disease - it's a symptom of many possible diseases...curing it would require fixing all sorts of odd problems - none of which seem to be listed?!? Curing migrane would require getting involved with seratonin inhibitors in the brain...this would have to be a substance capable of crossing the blood-brain barrier. Such a substance should be regarded with EXTREME caution! In short - if this stuff did what it said - it would be capable of doing untold amounts of harm too! If you used it to cure your Arthritis and it started leaching into your brain and messing with your seratonin levels - the consequences would be horrific!

Where is the list of side-effects. No change that you do to the body comes without changes elsewhere. If it's curing one thing (say your migrane) then whatever effect it has on stimulating the growth of new cartilage in osteoarthritis would cause who-knows-what joint changes in people who have no cartilage problems to start with!

If this stuff works as advertised - it's lethally dangerous and I wouldn't want to be within 50 feet of an opened bottle! If it doesn't work (as I STRONGLY suspect) - then don't buy it because it's snake-oil.

At best, this is a mild pain reliever - probably more for psychosomatic reasons than anything else. My mother uses 'witch hazel' to relieve her migranes - it's very clear that it's not doing anything but acting as a credible placebo for her - so I'm not going to tell her that it's useless. This stuff is likely doing the same thing.

Sorry - but science CAN discuss these kinds of matter.

SteveBaker (talk) 14:27, 15 December 2009 (UTC)

Out of curiosity several Shell lubricants contain salicylates (Alexia has the most check Google) and we did sometimes come across people abroad massaging it into arthritic joints apparently with some benefit (obviously, this is not medically safe, but aspirin is a salicylate of course). Conventional analgesics can be absorbed by the skin, and do occur in tree bark etc but as I think Steve's said before the ones which work are sold as medicine and the ones which don't work are snake oil. --BozMo talk 14:46, 15 December 2009 (UTC)

...and this stuff might (maybe) work as a pain reliever. But that's not all that it claims. It's actually claiming to CURE a wide variety of incurable conditions. If you want a topical salicylic acid (asperin) cream then buy something like 'Aspercreme' - which does contains exactly what you need and is unlikely to add a bunch of other things that you don't need. SteveBaker (talk) 15:22, 15 December 2009 (UTC)

Just out of curiosity, Steve, do you call your mother really fucking stupid for using the witch hazel? You're a smart guy and I appreciate your knowledge, but that was really fucking rude. Matt Deres (talk) 15:11, 15 December 2009 (UTC)

As a side note, I do call my mother "fucking stupid" when she fails to read the scientific papers I download for her questioning the efficacy of the various CAM products she likes to buy. I tend to get many thought terminating clichés in return for it, but some people just can't be taught it seems, even the organism from which I'm derived. --Mark PEA (talk) 18:03, 15 December 2009 (UTC)

No - I don't - but then she doesn't wait for a question about the efficacy of a dubious commercial product on a science reference desk and then tell us we can't answer the question because it's culturally sensitive (and the two asterisks don't stand for 'u' and 'c' - that would be rude). SteveBaker (talk) 15:17, 15 December 2009 (UTC)

omg!! I've been insulted by the great SteveBaker! That's really made my Christmas! By the way, my rheumatologist told me to take glucosamine for my joints. I always assumed if a qualified medical doctor told me to take a tablet then it would work. Is that not the case now? The original question, by the way, wasn't about the "efficacy" of a product, it was "where can I find more information on", and in that case the correct response should not have been to refer to "snake oil", but to the product website. I guess I'm as guilty as the responder as assuming cultural norms here. --TammyMoet (talk) 16:10, 15 December 2009 (UTC)

Firstly - I'm fairly sure your rheumatologist didn't say that glucosamine would "cure" your arthritis (certainly not osteoarthritis). Secondly - read our article on Glucosamine...pay special attention to the bits about the results of clinical trials. SteveBaker (talk) 17:22, 15 December 2009 (UTC)

We mis-understood the question the OP was asking, and devolved into a tangential discussion. Nimur (talk) 21:36, 16 December 2009 (UTC)

All of you have misunderstood my question. I want information on shatika, which is a problem with the nerves. I do not want information on the herbal remedies etc-Shahab (talk) 16:38, 15 December 2009 (UTC)

Well, the trouble is, there is no such English language word as "Shatika" - so all we could do was to go by the link you posted. That said - I wonder if you mean "Sciatica" (pronounced "sigh-attic-a") - which is a fairly common nerve condition (which that oil won't cure either!). If that is the case - then read our excellent article: Sciatica. Sadly, we're not allowed to give medical advice - so we may not be able to help you much more than that unless your interest is of a more general nature. If you have sciatica (or anything that you think MIGHT be sciatica) - then you need to consult a doctor. SteveBaker (talk) 17:14, 15 December 2009 (UTC)

Thanks. Sciatica was what I was looking for. Regards.-Shahab (talk) 17:24, 15 December 2009 (UTC)

Oh well - it was a bumpy ride - but we got there in the end! :-) 18:09, 15 December 2009 (UTC)

Acetone/Water Mixtures: Flammability

Greetings! Acetone is a flammable liquid. 1 % acetone in water is not flammable. At what concentration (v/v or w/w) are liquid water/acetone mixtures flammable? And at what liquid mixture ratio is the vapor flammable? (everything under standard conditions). I have been searching, but these data seem to be hard to find. Thanks for help! Grey Geezer 09:21, 15 December 2009 (UTC) —Preceding unsigned comment added by Grey Geezer (talk • contribs)

One type of answer (which leads to more questions!) is "whatever liquid ratios give acetone vapor concentration between the lower flammability limit and the upper flammability limit". Assuming it's actually the evaporating (and rapidly so, given the heat of the flame) acetone that's burning, you need to know the Lower flammability limit. The added water means some of the heat is used to evaporate that rather than acetone (reduces the efficiency of the self-perpetuating flame) and to dilute the air/acetone vapor with water vapor (affects the lean/rich mixture required to burn). I have no idea the specifics for acetone, but those are "one level deeper" into how I understand the issues involved. DMacks (talk) 09:40, 15 December 2009 (UTC)

Depends on the liquid temparature too. My copy of the rubber company handbook has vapour pressure curves for acetone above mixtures of acetone water but in practice it is going to be tough to calculate, and flash points etc in reality depend heavily on geometry however we try to standardise them. The only help I can think of is that these kind of numbers are easily obtained for ethanol and ballpark acetone might be similar. Cold brandy is hard to burn warm brandy will sustain a flame easily. So brandy at say 20C (and 40 degrees proof which is 20% alcohol is marginal). Guess acetone might be something similar? --BozMo talk 10:06, 15 December 2009 (UTC)

I would be extraordinarily careful about any attempt to generalize from one flammable liquid to another. The boiling point of acetone is only 56°C, compared to ethanol's 78°C; at room temperature the vapor pressure of pure acetone (nearly a third of an atmosphere) is roughly triple that of ethanol. Meanwhile, the lower explosive limit of acetone (2.6-3.0%) is lower than that of ethanol (3.0-3.3%). What you might try searching on is something like air-water partition coefficient acetone. Google scholar or PubMed will turn up a number of results. I'm not in my office at the moment so I can't get at the journal articles that are hiding behind paywalls, but there are some likely hits there if you're coming from a university with suitable subscriptions. TenOfAllTrades(talk) 16:40, 15 December 2009 (UTC)

I further searched my question with lower flammability limit but still did not find the answer. It surprises me that this piece of data seems to be nowhere available. If TenOfAllTrades comes up with a number and a reference, I could look myself. Grey Geezer 11:52, 16 December 2009 (UTC) —Preceding unsigned comment added by Grey Geezer (talk • contribs)

What are the arm blades of a preying mantis made from?

I've seen videos of the large preying mantises stabbing or slashing open rodents and birds with them. I suppose that they're probably made from a similar substance to the rest of the mantis's exoskeleton, but are they toughened or hardened somehow? Also, does the mantis have to do anything to keep them sharp? --95.148.104.205 (talk) 09:23, 15 December 2009 (UTC)

It may have been done initially with pun intended, but the proper spelling is praying, referring to the folded arms/prayer-like stance. DRosenbach ^{(Talk | Contribs)} 14:17, 15 December 2009 (UTC)

AFAIK, "blades" of the grasping forelegs are made of the same thing all insect exoskeletons are made of: chitin + protein matrix + calcium carbonate. Chitin by itself is somewhat similar to cellulose, but the addition of the other two components makes it much more rigid. Now, as far as the sharpening goes, mantises spend really a lot of time grooming their forelegs; but I am not sure at all if that contributes to the sharpness of the spines on the forelegs or is just meant to keep them clean. Anyway, keep in mind that any mantis molts a number of times before it reaches adulthood, and the entire exoskeleton is replaced every molt. --Dr Dima (talk) 10:34, 15 December 2009 (UTC)

Tree question

I am ok at felling trees in a given direction but I have a tricky one. The tree is on the bank of my moat, and is leaning over the moat by about 30 degrees (slowly falling). The moat is 6 m wide and the main tree truck is about 18m high (most of the canopy is gone so it approximates to just a trunk). I do not want to be fishing a tree trunk weighing a number of tonnes out of a 2m deep moat so I want to fell the tree so that the bottom of the fallen trunk is at a good distance from the stump. If I cut the tree at a given height above the ground how far away from the tree stump will the bottom of the trunk be at impact on the ground? Can I improve this by varying the slope of the cut? Any other ideas on how to get the trunk well over the moat?--BozMo talk 10:17, 15 December 2009 (UTC)

A photograph would help!

It doesn't matter how high up you cut it - the tree rotates about the point where you cut it until it's pretty much horizontal - and then pretty much falls vertically. If the fibreous wood doesn't break cleanly - then the trunk may even stay attached to the top of the stump and cutting it up higher just makes for a lot more grief - and makes what I'm about to suggest even more difficult. But a lot depends on how clean the break is and how top-heavy the tree is. IMHO, you're not going to get the trunk to fall more than maybe half a meter from the stump, no matter what you do.

If the geometry of the situation is as you say then you need to fell the tree so that if falls at right angles to this 'moat' - cutting it as close to the ground as is reasonable. If it's already leaning by as much as you say - you have no chance of making it fall in any other direction anyway.

If you're right about the dimensions then about 12 meters of tree will be on the far side of the moat with 6 meters dangling in fresh air across the moat. In theory - if the tree were of uniform thickness - the 12 meters out there on dry land would be plenty heavy enough to stop the other 6 meters from falling into the water. However - if the tree tapers strongly then it's possible that the bottom 6 meters will be heavier than the topmost 12 meters - and then the heavier bit might dip into the water - but at least you could loop a rope over the top of the tree and with a modest amount of weight - pull it down so it's horizontal.

Once it's down - if you don't have heavy machinery to haul the trunk 6 more meters until it's all on level ground - then I suggest that you prepare some rollers (maybe some nice round logs) on the far side of the moat for the tree to land on that would make it easier to pull it away from the water. If the tree's trunk is nice and smooth and round - you could probably use a fulcrum close to the water's edge to rotate the tree so that it's almost all on land anyway.

Whatever you do, don't start cutting the top of the tree into logs until the bottom is pulled clear of the water because as soon as you remove weight from the top of the tree - the bottom will be more likely to fall in!

Also, I would prepare for the worst by tying some heavy ropes or chains to the base of the tree a few feet above where you intend to cut it - BEFORE you cut it down - so that if it does end up in the water - you at least have something to haul it out by.

Good luck!

SteveBaker (talk) 14:06, 15 December 2009 (UTC)

The real worry about tree felling as far as I'm aware is if the tree doesn't just angle over still connected to the stump but breaks away, in which case the base of the tree would come towards you rather than go further over the water. So yes the best you can do is cut it near the base. If you can strip off the branches for the first 6 meters it mightn't be too hard to winch it out after you're finished. Or there may be some heavy canvas or a board you could put down to make it slide over the other bank easier. The only advantage I can see of cutting it higher up is that the bit over the moat will be lighter. Dmcq (talk) 14:21, 15 December 2009 (UTC)

Yep, its a big Ash and will split violently. But by the time it does the canopy must have momentum away from the bank. Perhaps if I undercut the far side and over cut the bank side second I can get the whip to go the right way. My guess is there is at least six or seven metric tonnes of trunk there though so the sliding bit ain't going to be easy. --BozMo talk 14:50, 15 December 2009 (UTC)

The base of the tree can indeed kick backwards (because the tree would 'naturally' try to rotate about it's center of gravity - not about the bottom of the trunk) - but if you do it right, you don't cut all the way through the trunk - you leave enough wood there to act as a "hinge" to prevent that from happening - and to give you enough time to shut your chainsaw off and get far enough away from the falling trunk! But that hinge also ensures that the tree rotates about the top of the stump - so that end of the trunk will end up close to (if not still attached to) the stump. When you get it right, that hinge breaks through completely just as the tree gets horizontal. The angle of cut of the "notch" that you cut on the side where you want the thing to fall is what makes that happen. The depth of the cut on the opposite side (which actually brings the tree down) is what ensures that the "hinge" is the right strength. There is an art to doing it right. I suppose the if the hinge broke through before the tree got horizontal - it might slide a little away from the stump - but I can't imagine that being anywhere near far enough to make a difference here. SteveBaker (talk) 14:54, 15 December 2009 (UTC)

I see lots of trees removed from backyards or parkways near homes, and the tree companies almost never just cut it down and let it fall when structures, fences, or sidewalks are anywhere near. Instead, they strip the tree down to the main trunk and a few main uprights by cutting branches and using pulleys tethereed to the main trunk to lower the branches to the ground. Then they cut the main trunk into short manageable sections which are lowered to the ground by pulley attached to the bucket the cutter works from. It is a few minutes work rather than one big boom. If you cut it down in one or two pieces, you would still need to cut it up for firewood or to go in the chipper. Standard tree removal would be easier than trying to cut up a tree which fell in a water filled ditch. Forget trying to be Paul Bunyan. A tree can spring back and kill the person cutting it. The impact of a large tree hitting the ground can jar nearby structures and knock things off shelves, or crack plaster. YouTube and America's Funniest Home Videos are full of unexpected outcomes of amateur tree felling. Call a professional, which might be affordable if you can afford something which needs a moat to protect it. Edison (talk) 15:07, 15 December 2009 (UTC)

Indeed - but we're told that this tree is 18meters tall(!) so climbing up it to bring it down in sections would be tricky - and it's leaning at 30 degrees out over a freezing cold moat...so lowering the topmost sections to the ground ain't easy either. Also, operating a chainsaw while balancing 50 feet off the ground in a dead tree over a cold wet moat is a life-threating situation that I absolutely won't recommend! SteveBaker (talk) 15:14, 15 December 2009 (UTC)

See Cherry picker. Pros do climb healthy trees, but more often the work safely from the bucket. The reach can be quite long, and the 3 foot sections can be lowered individually. 18 meters=18 pieces of wood. No big challenge or drama at any point. Edison (talk) 17:08, 15 December 2009 (UTC)

The critical question here (and something you don't KNOW the answer to) is whether the top 12m of the tree is heavier than the bottom 6m. If it is - then you need to have it land on a nice thin-but-hard fulcrum - close to the center of gravity of the tree. If you had it balanced perfectly on something like a large log - then the effort to rotate it 90 degrees so it's no over the water anymore would be fairly small - even if the weight of the trunk were many tons. Sadly, you can only guesstimate the center of gravity - so make your best guess and at least minimize the amount of pushing and shoving you'll need to do. Personally, I have a couple of block-and-tackle sets which allow me to haul very large tree trunks over short distances - so even if things didn't come out perfectly, it would still be a do-able job for one guy to get the entire trunk over dry land. But like I said - that assumes that the center of gravity of the trunk is more than the width of the moat from the cutting point. The lower you cut it - the more likely that is to be true. But there is absolutely nothing you can do to make a multiple ton tree jump six meters sideways and avoid the moat! SteveBaker (talk) 15:14, 15 December 2009 (UTC)

...and all of this discussion is why, if it is important for a tree to fall in a particular place (or especially if it's important that a tree not fall in a particular place) one should seek the services of a professional. The pros have all of the equipment and training to do the job right — and insurance, just in case they don't. Look in your telephone listings under "Arborists" or "Tree removal". A wise man knows when he's in over his head. TenOfAllTrades(talk) 16:08, 15 December 2009 (UTC)

...to be fair I have used tree surgeons for three of the larger dead trees I needed doing this year but those were ones which would have hit a road or an eleventh century church by our boundary. Aside falling in a moat or killing myself with a chainsaw (and I do quite a bit with a chainsaw myself) the worse case with this one is that I lose a load of firewood. The nearest building is a long way off. There may be some damage to a 900 year old scheduled moat too but that will happen for sure if I leave the tree to fall under its own steam. But Steve is probably right there is no way to get it to jump. --BozMo talk 16:43, 15 December 2009 (UTC)

If it is cut via cherry-picker bucket in short manageable pieces there is no damage to the ancient moat. I'm sure you are a smart feller and will consult a professional rather than random persons on the internet of unknown qualifications. Edison (talk) 17:20, 15 December 2009 (UTC)

I'll second that, the only posters in this thread you should be listening to are the ones telling you to get someone else to do it. Yes, you can get the tree to "jump" away from the stump—if the wood is sound you could probably fall it in any direction you wanted, despite the thirty degree lean. Do not pay attention to any of the advice above, those giving it have no idea what they are talking about.—eric 18:42, 15 December 2009 (UTC)

Its ok thanks. I asked for their advice because I wanted it and I am happy with some of the ideas. Sculpting trees in a town centre is a bit different from a country garden with lots of space and several hundred mature trees in it. But a cherry picker might be able to get there in the summer. --BozMo talk 18:57, 15 December 2009 (UTC)

EricR & Edison: Those are ridiculous statements. For starters, I have been dealing with trees and chainsaws off and on for about 35 years - and I know my way around a block-and-tackle - and it sounds like our OP has been there and done that too. Since we're both people who actually DO know what we're talking about, the advice to ignore all of this, throw up your hands and run to an overpriced professional is silly. This is a simple matter of physics - and that's exactly the kind of thing the science desk is here to discuss. We have medical disclaimers and legal disclaimers - but no tree-surgeon-disclaimers. I'd like to hear EricR's idea of how you get a multiple-ton tree to fall in the opposite direction to which it's leaning (at a 30 degree angle - over water, no less!) - or to jump 6 meters sideways. That should be good for a laugh. This is fairly elementary physics. Having said that, a Cherry Picker could let you take it down in sections if you can find one that can lean far enough out over the water whilst reaching up that high - and not damage the edge of the moat. SteveBaker (talk) 19:11, 15 December 2009 (UTC)

Not ridiculous at all, and civility is always appreciated. Edison (talk) 00:27, 16 December 2009 (UTC)

We certainly have no way of knowing if there is a way to drive a large truck near the tree. Foresters in my town have them in various sizes, small to HUGE with a very long reach. Tree felling is one of the most dangerous occupations, and even people who "have been dealing with chainsaws for 35 years" get killed in large numbers every year. Edison (talk) 20:25, 15 December 2009 (UTC)

There still remains a difference between the pro and even a seasoned amateur, and there's a potentially wide gap between someone who has 'been dealing with trees and chainsaws off and on' and someone who does the job every day for a living. My grandfather was a shop teacher for a couple of decades, then went on to build and operate a small sawmill and woodlot. He felled, cut, dried, and planed the cedar for my parents' back fence. When the time came to take down an awkwardly placed tree near one of his buildings, he still called a pro.

The pros have the right specialized tools (not just 'close enough'), and years of daily practice. The pro comes with a crew who know the job, and wear the right safety equipment; they're not your buddies from work (long on enthusiasm but short on experience, and who lack any sort of insurance coverage) who are in it for the free beer and pizza afterward. If the job requires really specialized equipment (like a cherry picker), the pro probably gets a discount on the rental. (The pro is also less likely to inadvertantly tip the cherry picker into your moat.) While I certainly would recommend avoiding an 'overpriced' professional (by all means get more than one quote!), I can't emphasize enough the value of real professional experience. TenOfAllTrades(talk) 20:35, 15 December 2009 (UTC)

Why don't we have tree-surgeon-disclaimers? Bus stop (talk) 20:57, 15 December 2009 (UTC)

The Schools Wikipedia says "not intended ... to be used in any way as a basis for behaviour" which would include trees... --BozMo talk 22:24, 15 December 2009 (UTC)

Steve, if it's a simple matter of physics then try this simplest of machines. All i can do here is relate a story about this guy. Teaching a class to professional fallers, he boasted that he could wedge over any tree that had good sound wood. Later, someone spotted a tall cedar, leaning way over backwards, and bet that this was one tree he could not wedge over. It was a set-up, he pulled a couple of high-lift wedges out of his bag and went to work. He would whittle away at the back cut, then tap on the wedges for a bit while watching the top of the tree. He added more wedges—driving some sideways near the holding wood and stacking others to get more lift. After about an hour of pounding on the wedges he had lifted the tree far enough that it fell in the direction he wanted—and won a steak dinner from the class.

Now a second-hand story really doesn't belong on the reference desk, but i hope it illustrates the difference between a professional and someone who, since they know a little bit of physics, thinks they can teach something as dangerous as timber falling. Based on your posts above, it sure doesn't sound like you've "been there and done that".—eric 01:10, 16 December 2009 (UTC)

There are nonetheless limits to what can be done with wedges, I use them a lot. But in this case the hero of the story would have drowned or died of hypothermia...--BozMo talk 13:07, 16 December 2009 (UTC)

And for a laugh, don't forget to go on youtube and search for tree felling accidents. I personally would agree that if there is any chance of damage to property, you should seek the help of an expert. Even if you are familiar with a chainsaw, if this is the 1st big tree you are cutting down, they say you learn from mistakes and in a situation when a mistake can be dangerous or expensive, it's better to let someone who has learned already do it. Vespine (talk) 23:48, 15 December 2009 (UTC)

We don't have tree surgeon disclaimers, but we do point out alternative methods that are sometimes used, and there is no reason we cannot counsel calling in someone with special equipment. What Steve says all sounds accurate if there are no nearby structures that could be harmed by an object weighting many tons falling on it. But many tree fellers have been surprised in unfortunate ways when the saw blade binds and they stick around too long trying to rescue it, or when it kicks back, or when the crown hits and it springs back. The timber industry has about the highest mortality rate among occupations. If you just fell the tree across the moat, it is likely to leave a depression in the other side of the moat when it hits. The portion hanging over the water after felling could be sawed off a few feet at a time in manageable hunks, and fished out by a rope you thoughtfully attached ahead of time. That part of the cutting could await warmer weather, so if you fall in the water is not freezing. Pros have lines, pulleys, and tree gaffs and are comfortable using them, as well as assessing the soundness of portions of a tree if climbing is chosen. They routinely take down much larger trees without drama, in small pieces. They have forestry bucket trucks which can reach a 95 foot working height or a lesser height with some lateral reach. Sometimes hard frozen ground is preferable to avoid ruts. Edison (talk) 00:27, 16 December 2009 (UTC)

I must admit thinking abut it I'm rather concerned that the poster thought the tree would jump in the direction it was falling rather than being worried about the trunk breaking off and coming back at him. If felling a tree you should have some idea of how the tree might behave as it falls and of possible problems. SO yes I'll add my voice to get a professional. Dmcq (talk) 01:24, 16 December 2009 (UTC)

Actually I've done a fair number of trees. The end of the trunk always ends up hitting the ground some small distance from the stump in the direction of the tree falling (unless the canopy catches other trees). Getting out of the way is not generally a problem especially as the last bit is always done with a sledge hammer and wedges rather than with a running chainsaw. Spring back is the commonest cause of fatalities with chainsaws though and I haven't done many at any angle. I will upload a couple of photos but its snowing now. --BozMo talk 12:27, 16 December 2009 (UTC)

That's good. The reason it will end up a little from the tree in the direction the tree falls if it is done right is that the trunk only parts from the stump after it has gone nearly horizontal, so yes as you say the momentum after that point will carry it away from the stump. I'd be surprised if you can get much distance at all that way, but I wonder at what angle one would get the best effect. There might be something about felling trees on the web about it. Dmcq (talk) 14:15, 16 December 2009 (UTC)

tree hanging over moat

Here is a view of the tree from the corner of the moat, in high res you can just see ice on the near water. The tree is the obvious central one leaning over the water. Not remotely huge as trees go (about 75cm diameter trunk, so maybe 3-4 tonnes rather than 6-7 above) but still hard enough to lift. The angle at the base is close to 45 degrees and the trunk bends upwards, making wedges implausible even without the water. The moat is deceptively deep. There are quite a few similar trees. --BozMo talk 15:07, 16 December 2009 (UTC)

That looks nasty. The wood may not be good, bits may fall off, it may get lodged in a trees opposite, there's stuff all around it no nice way to retreat, not nice to clean up the bottom of the trunk so it doesn't get stuck in the moat. It looks to me like everything people warn about. And you've a load of them. I'd take professional advice, though I just had a look at a few videos and they looked pretty scary the precautions they weren't taking. Dmcq (talk) 15:52, 16 December 2009 (UTC)

Hmmm - a picture is worth a thousand words! Firstly - I did some measurements on your image - and there is no way that the chunky "trunk" part of the tree is three times the width of the water as you first said...it's at best twice as wide - probably less (we can't really see where the bank is opposite the tree - so it's almost certainly wider than I measured). Your estimate of a 30 degree lean angle is probably about right (although it's hard to get a decent vertical cue out of that photo). But also, the curve at the bottom of the trunk that makes it start out over the water almost horizontally makes it hard to cut a proper notch to get the tree to fall exactly the way you'd want - so it's probably going to go down at some non-optimal angle. That really changes things because now there is really no way that the bottom end of the tree can stay out of the water - and a very good chance that the whole thing will end up in the drink. Also, the way the bottom end of the trunk curves is going to be bad news for dragging it out of the water afterwards. Do you have access to a tractor or something? At this point, I think I'd tie some heavy chains around the bottom end of the tree - cut it down and let it fall where it may and then use the chains and a lot of brute force (and a heavy block & tackle or a tractor!) to pull it out of wherever it lands. It's either that or use a cherry-picker and take it down a bit at a time as others have suggested - but the terrain around there looks kinda rough for that kind of machinery to get in there and the lean of the tree and the placement relative to the water will make that be a difficult (and therefore expensive) operation. SteveBaker (talk) 19:30, 16 December 2009 (UTC)

Fair enough. It was easy to get the height (I can do simple algebra) but the width of the water was a guess and it could be 7m. I do have an Ordnance Survey site map from the listing somewhere. But back to my first idea: what happens if I cut it six foot up and a fair way over the water?--BozMo talk 19:43, 16 December 2009 (UTC)

Movement of the sun and moon around the sky

So, in the Northern hemisphere, the sun rises in the east, moves in a clockwise direction through the sky (and is at its midday peak in the south) and sets in the west. The moon does the same. Am I right so far? So what happens in the southern hemisphere? Does the sun still rise in the east? Is it at the north at midday? Does it go in an anti/counter-clockwise direction to set in the west (if it sets in the west?)? And what happens on the equator?

In the Northern hemisphere, stars move around the Pole Star - but what direction do they circle in - clockwise or anti/counter-clockwise?

Thank you for helping.81.159.89.69 (talk) 11:44, 15 December 2009 (UTC)

The cause for all these apparent motions, including star movement, sun rise, and sunset, is Earth's rotation. (The moon also adds a non-negligible extra detail due to its orbit around us, and the Sun also adds a smaller variation because of our orbit around it). But the most important factor here is Earth's rotation. Since Earth's rotation direction is the same everywhere on Earth, the apparent rise of the sun and moon are always in the east; the apparent direction is always the same - counterclockwise if you're facing north (clockwise if you're facing south). In the unique case of polar regions, the midnight sun throws another neat variation, in that the summertime sun never gets low enough to sink below the horizon; but it still "wobbles" in a circular path. The equator doesn't really behave very specially, except that the sun is directly overhead, approximately at the zenith, on noon of the equinoxes. As far as where the sun is at its midday peak, this depends on your latitude and the current season. Nimur (talk) 13:25, 15 December 2009 (UTC)

edit conflict Because, from a bird's eye perspective of the plane, so to speak, of our solar system, the earth rotates on its axis in a counter-clockwise fashion, the celestial entities (sun, moon, planets, stars) seem to orbit us in a clockwise fashion. Therefor, things rise in the east and set in the west. For one living in the northern hemisphere, solar/lunar "orbits" manifest as short days, with rising and setting occurring south of due-east and -west and the celestial entities don't travel too much into the southern sky. For the same northern hemispherer, summer manifests as long days, with the celestial bodies rising way north of due-east and setting way north of due-west and traveling three sides of the sky (east, south + west). Mid-day, by definition, presents as the sun in the exact middle of the sky in an east-west dimension, but the north-south aspect of the suns position at mid-day will depend upon the time of year (n.b. mid-day here is defined as the time from sunrise to sunset divided by 2). I will not speculate about what occurs in the southern hemisphere, because its quite easy to allow a minor error in calculation to become a tremendous error in conjecture. DRosenbach ^{(Talk | Contribs)} 13:30, 15 December 2009 (UTC)

Another interesting bit about latitude and the sun's midday position: it's a generalizable rule that the sun is southward in the northern hemisphere and northward in the southern hemisphere, unless you're in the tropics. Between the Tropic of Cancer and the Tropic of Capricorn (those lines of latitude equal to the Earth's angle to the ecliptic), this rule can be broken. At the northern summer solstice, all of the northern hemisphere south of the Tropic of Cancer sees the sun to the north at midday. In fact, at the equator, the expected lengths of day and such get extremely odd: the sun is highest in the sky near the equinoxes, lowest at each solstice. At Quito, Ecuador, the longest day of the year is near the December solstice (no surprise), but there's another maximum at the June solstice, and the minima are in April and August.[1] I expect that shift from the equinoxes is driven by the Earth's orbital eccentricity (the Earth is farther from the sun in June than in December). — Lomn 14:07, 15 December 2009 (UTC)

It's altogether easier to imagine that you're standing on the surface of a spinning ball - with everything else being more or less stationary! The ball takes 24 hours to spin once. (Which is unsurprising - because that's really what's happening.) SteveBaker (talk) 13:45, 15 December 2009 (UTC)

They say a picture is worth a thousand words, in this case an animation is even better. Download an open source application called Stellarium (computer program) and have a play. Firstly set your own location and play with the time controls, this will give you "bearings" of where and how the sun rises and sets, and where the stars rotate. Once you have a grip on what you are looking at, change your position to anywhere else in the world, the poles, the equator, anywhere in between, and play again with the time controls. Vespine (talk) 23:19, 15 December 2009 (UTC)

What happens when you mix hydrogen peroxide and liver?

Biology —Preceding unsigned comment added by 68.146.63.129 (talk) 15:04, 15 December 2009 (UTC)

In respect to physiology or culinary arts? H₂O₂ will bubble with oxygen release when contacting the blood of the liver (liver is very bloody, as it contains vascular sinusoids). DRosenbach ^{(Talk | Contribs)} 15:20, 15 December 2009 (UTC)

Depends how the liver is prepared. This is a common high-school bio experiment, so I'll not comment further. DMacks (talk) 17:44, 15 December 2009 (UTC)

I let myself correct your link, Drosenbach. --Ouro (blah blah) 18:00, 15 December 2009 (UTC)

I let myself correct your grammar, Ouro. :) DRosenbach ^{(Talk | Contribs)} 19:29, 15 December 2009 (UTC)

I had to check, what an error! Thank you! --Ouro (blah blah) 17:46, 16 December 2009 (UTC)

Earth Changes

How valid are some of the predictions in this article? Are they even possible? Are there any notable scientists today who vaildate some of the changes predicted here? --Reticuli88 (talk) 15:40, 15 December 2009 (UTC)

Not very - though I hasten to say it is a good article dealing well with the subject. The last couple of lines answer most of your question: "Prophecies of Earth changes have been described as a form of scientism, in which terminology and ideas borrowed from science are used to rationalize non-scriptural apocalyptical thought based on visionary experiences. David Spangler, a leader of the Findhorn Foundation spiritual community, described prophecies of Earth changes as an expression of collective fear and anger, rather than as foretelling of actual future events."

Clearly some predications may sometime come to pass; if sea levels rise, if there is a major earthquake or volcanic eruption. But the absence of real scientific underpinning tends to be the give-away. --Tagishsimon (talk) 15:49, 15 December 2009 (UTC)

How do we know the speed of light is constant?

We can measure the speed of light and observe that it has not changed between our measurements, but how do we know that the speed of light has not changed over the course of time? Or how do we know that the speed of light is not a local phenomenon, resulting in our speed of light being at least a little different then the speed of light in another star system or galaxy? 65.121.141.34 (talk) 15:45, 15 December 2009 (UTC)

The questions you ask are good ones, and physicists do think about what effect a changing speed of light would have, and whether we could observe such variation. While there is no good evidence of a variable speed of light, we do have an article on the topic: Variable speed of light. -- Coneslayer (talk) 16:23, 15 December 2009 (UTC)

The deal is that the speed of light is built into so many other parts of physics that the way things like the fusion reactions in stars work would be noticeably different if a different speed of light applied. When we look out at things that are a long way from us - we're seeing them as they were a long time ago. If the speed of light was significantly different than it is today - we'd be able to tell because we'd see things like spectral lines representing the emission and absorption frequencies of common elements being wildly different than they are today - or stars of a particular color having different 'ingredients' than stars of that color that are close to us. That same reason also explains how we know that the speed of light is the same in places a long way from us. I suppose that VERY small changes might somehow sneak by - but it would have to be a rather insignificant difference for it not to be somehow measurable. SteveBaker (talk) 17:04, 15 December 2009 (UTC)

The speed of light was also measured from a binary star, and no difference in the speed was detected when the star was moving toward, or away from us. I believe this was the first direct evidence of the constancy of the speed light. Ariel. (talk) 07:30, 16 December 2009 (UTC)

See Michelson–Morley experiment for that. --Stephan Schulz (talk) 08:07, 16 December 2009 (UTC)

At what distance was the binary star? Would a change of 0.1% per 1,000 lightyears be detectable using that method?

Hold on - this question got derailed in the middle there. This isn't the usual question of: "Is the speed of light independent of the motion of the observer relative to the source?" (Yes, remarkably, it is). That's what you'd use a binary star for - and it's what Michelson & Morley proved. No - this question asks whether the speed of light the same now as it was (say) a few billion years ago - and is it the same here, in our solar system as it is in (say) a neighboring galaxy? Michelson & Morley didn't attempt to show that - and a binary star doesn't help you much with that either. As I said - you really have to look at the secondary effects of the speed of light - comparing the diameter of the event horizon of a black hole to it's mass, for example. As I said before, I'm pretty sure that any change in the speed of light at long distances or in the distant past would produce extreme weirdnesses in the spectral characteristics of distant objects that we simply aren't seeing. So I believe it's fairly safe to say that we don't believe that the speed of light has ever been different or is different in different places. SteveBaker (talk) 03:22, 17 December 2009 (UTC)

Interpreting life expectancy

If I am a member of a group with life expectancy of 80 years and I am 25 years old, should I expect to leave more or less 55 years? Or does it means that children born today could expect to live more or less 80 years? Or people dying today are on average 80 years old?--ProteanEd (talk) 17:49, 15 December 2009 (UTC)

Given the development of medicine and technology you might live past one hundred. Given the development of ways to make others suffer, hell knows. --Ouro (blah blah) 17:53, 15 December 2009 (UTC)

WMDs have been around for decades and, in the grand scheme of things, very few people have been killed by them. I don't think their existence has a significant impact on life expectancy. --Tango (talk) 17:59, 15 December 2009 (UTC)

Usually life expectancy refers to life expectancy at birth. So it is talking about people born today. If you want more detailed information you need a life table (there are life tables available online for free for various populations) - that will show how long people born at different times can expect to live. Life expectancy increases as you get older because there is no longer a chance of you dying before your current age. So, if life expectancy when you were born was 80 years then you can expect to live longer than 55 years (assuming you are an average members of that population in terms of lifestyle, etc.). Life expectancy for people born now doesn't say much about how long you will live. --Tango (talk) 17:59, 15 December 2009 (UTC)

Bear in mind that such a life expectancy is the calculated average expected for the group overall. There are always variations above and below the average, and unforecastable accidents (such as terrorist bombs) may or may not have been taken into consideration. The predicted life expectancy of the cadre you are in cannot say anything very definite about your individual life expectancy; a detailed individual health and lifestyle analysis would be necessary for that, and-- Oops! Watch out for that meteorite!! 87.81.230.195 (talk) 19:42, 15 December 2009 (UTC)

I strongly suspect that terrorist bombs and meteorite strikes are but a minuscule impact on life expectancy. 65.121.141.34 (talk) 19:51, 15 December 2009 (UTC)

I agree. I wrote this on Talk:Main Page but it's of relevance here:

This is somewhat morbid/grim so don't read if you are uncomfortable with that but as has been kind of hinted at, deaths due to natural disasters can relatively easily exceed death tolls due to terrorist attacks or building fires, and unfortunately relatively often enter into the quadruple digits (look at the earthquakes list for example [2]). Just this year we had the 2009 Samoa earthquake and resulting tsunami (death toll possibly exceeded any single event you mentioned) which occured on the same day as the 2009 Sumatra earthquakes (alone over 1000). And a few weeks ago we had 2009 Jeddah floods which was in the triple digits (and deaths during the Hajj are unfortunately not uncommon). Can't remember if we had Typhoon Ketsana (2009) but that's over 600 if we did (and worse therefore then any other terrorist attack so far bar September 11 [3]). Earlier this year, I'm pretty sure we had the Black Saturday bushfires which again possible resulted in more deaths then any single event you mentioned. As Boz said, the 2004 Indian Ocean earthquake and resulting tsunami is the worst that we've had. Hopefully we'll never exceed that in a long time but unfortunately it could happen, List of natural disasters by death toll is perhaps poignant reminder of that. P.S. Just to be clear, I'm not trying to downplay the impact of terrorist attacks simply pointing out that in terms of deaths, they pale in comparison to many natural disasters

Of course even natural disasters are a small percentage of deaths. In much of the developed and developing world, you much more likely to be killed in an road accident for example. P.S. The events that I didn't name there are the recent Baghdad bombings, the recent Pakistani bombings and the night club fire. Nil Einne (talk) 13:18, 16 December 2009 (UTC)

And then, of course, there is old age. The vast majority of people in the developed world die of age related diseases. The majority is not so vast in the developing world, but I think it is still a majority. --Tango (talk) 16:58, 16 December 2009 (UTC)

See actuarial table. I believe the article (and the first actuarial table you read) will answer your question fully. Comet Tuttle (talk) 22:53, 15 December 2009 (UTC)

Why am I able to see depth in this video?

what is the science behind this please. --Reticuli88 (talk) 18:21, 15 December 2009 (UTC)

When you cross your eyes and get the images (which are slightly different) to overlap what is happening is one eye is looking at one image and the other eye at the other image and brain is interpreting it as if they are both looking at the same thing. Your eyes seeing slightly different things is one of the main ways we perceive depth (see binocular vision). --Tango (talk) 18:42, 15 December 2009 (UTC)

We have an article on these of course: stereogram. Jkasd 18:48, 15 December 2009 (UTC)

Do you know where on the internet is there videos of moving stereograms? --Reticuli88 (talk) 18:55, 15 December 2009 (UTC)

A collection of stereograms can be found here. Scroll to the bottom of the page for 2 animated examples. Pim Rijkee (talk) 22:17, 15 December 2009 (UTC)

We have one here. It's a pretty interesting one since you can't tell what it is until you cross your eyes. (Besides reading the title.) Jkasd 04:32, 16 December 2009 (UTC)

plastic laminate

what makes up laminating plastic material?are the chemicals safe to use in the home ? —Preceding unsigned comment added by 173.88.240.10 (talk) 18:50, 15 December 2009 (UTC)

For woodworking, most "plastic" laminate is made of layers of paper bound together with epoxy. The chemicals used to bind this to the surface often have volatile chemicals in them and should not be sprayed without ventilation. If you're referring to the thin, sticky plastic used to cover books and posters, this is usually made of PVC with a layer of adhesive. Laminators using heat to make name badges or other objects may pose a risk if you burn the plastic. There are many ways to use a laminate material, so without more specific uses, the safety can't be evaluated effectively. Caltsar (talk) 17:07, 16 December 2009 (UTC)

Gallium

Where's a good place to buy gallium online? ----J4\/4 <talk> 19:39, 15 December 2009 (UTC)

It's available on Ebay. 10 gram lots of claimed 99.9999% pure Gallium have sold in the recent past for $29.11 and 100 g lots for $113 from a UK supplier. Also see Answers.com for the same question. [4] sells it for $1250/kg. Edison (talk) 20:14, 15 December 2009 (UTC)

But couldn't the sellers on ebay be lying? Also, is gallium toxic? ----J4\/4 <talk> 20:16, 15 December 2009 (UTC)

Toxicity for the pure element is still indeterminate for skin contact. 65.121.141.34 (talk) 20:34, 15 December 2009 (UTC)

Sellers on Ebay can always be lying. But if it is someone who sells a lot of similar products and has a very good rating, they are probably not lying. --Mr.98 (talk) 21:23, 15 December 2009 (UTC)

How would they check? Do gallium buyers generally have the equipment required to test its purity to that level? Vimescarrot (talk) 21:34, 15 December 2009 (UTC)

I assume people buying 99.9999% pure gallium are probably doing something with it that requires very pure gallium. I have no idea what that would be. If pure gallium were indistinguishable from garbage then they wouldn't need to bother buying pure gallium. Rckrone (talk) 22:02, 15 December 2009 (UTC)

United Nuclear has Gallium chunks available. Expensive, though—$15/g. --Mr.98 (talk) 21:22, 15 December 2009 (UTC)

Well clearly a home user is not going to be able to differentiate between 99.9% purity or higher -- though 99.5% purity could cause a significant change in physical characteristics that might well be noticeable. A quick search on Google does show Journal articles referencing gallium used at 99.999% purity, sourced from one of the main chemical suppliers, so I would accept that gallium at this purity does exist. There must be a particular feature of gallium or its extraction that makes it relatively easy to manufacture it at this relatively high purity. For other metals the difference between 99.5% purity and 99.99% purity could typically be a factor of 10 in price. Rjwilmsi 23:17, 15 December 2009 (UTC)

Do none of you ever bother to read the articles? :-P From Gallium

Electrolysis then gives gallium metal. For semiconductor use, further purification is carried out using zone melting, or else single crystal extraction from a melt (Czochralski process). Purities of 99.9999% are routinely achieved and commercially widely available.[17] An exact number for the world wide production is not available, but it is estimated that in 2007 the production of gallium was 184 tonnes with less than 100 tonnes from mining and the rest from scrap recycling."

&

The semiconductor applications are the main reason for the low-cost commercial availability of the extremely high-purity (99.9999+%) metal"

Then there's these in the external links pure Gallium crystals ~99,9999% picture in the element collection from Heinrich Pniok & Price development of gallium 1959-1998. And in the article, I noticed

High-purity gallium is dissolved slowly by mineral acids.

which may or may not be a good way to test purity.

However I have to admit I'm sceptical of these Ebay sellers. You can get a decent idea from feedback but it's far from perfect. Given the prices, I wonder if these people really need such high purity or are just buying it because it's cheap. What are they even using it for? Would someone in a research lab or other place where they may really need such high purity actually buy from eBay? It seems to me they're more likely to buy from an established supplier outside of eBay. Maybe the people know the claims are probably bullshit they just don't care? In other words while it may very well be that purity, I'm don't think we can go solely by the feedback. Taking a look at what else the people have purchased may help, since it may give you a hint what they're likely to be using it for.

Also looking at the feedback, e.g. if it's largely "delivered on time, looks great in my metal collection" or "received today, now I can get started on my perpetual motion machine" I wouldn't trust them to know what the purity is. If it's "just confirmed with mass spec and NAA that it's really 99.9999% purity" [5] [6] ref(yes I know this isn't gallium metal) or "wow I didn't really expect it to be genuine 99.9999% purity but I the results from the X-ray diffraction, SEM, AA, BET surface area, and ICP Spectrometry confirms it is" ref(slightly OT but maybe those will be useful to test the purity tool); well then you can think maybe they do know what they're talking about.

I also came across [7] which may be of interest Nil Einne (talk) 15:10, 16 December 2009 (UTC)

Southern Hemisphere deciduous forests

Why doesnt the southern hemisphere have more temperate broadleaf decidous forests?

There are some in South America (southern Chile and Argentina), and one deciduous shrub in Tasmania, Australia (Nothofagus gunnii), but apart from that, there isnt much. Whats preventing southeastern Australia (New South Wales and Victoria) from having a deciduous forest? The climate there definitely calls for one...

And what about Argentina, further north in the region between the Parana and Uruguay Rivers, and the Buenos Aires province. The climate there also calls for a deciduous forest, albeit different from that of the more southerly one. We can perhaps draw a comparison between the climate of that region (Parana...etc.) and that of the southeastern U.S. (Louisiana, Mississippi, Alabama, Georgia). Those states are predominantly made up of deciduous forests, with a few pine forests also thrown in. So, why doesnt the southern hemisphere have more deciduous forests? Any ideas...? Thanks! —Preceding unsigned comment added by 201.21.180.57 (talk) 21:21, 15 December 2009 (UTC)

How would deciduous trees of any kind spread to the Southern Hemisphere? They would have to spread gradually through the tropics from the Northern Hemisphere, and they don't survive in the tropics. So, barring human transport, there's no mechanism by which such plants would migrate to the Southern Hemisphere. --Jayron32 21:49, 15 December 2009 (UTC)

That argument is not valid, as deciduous forests are found all over the world: the question is, why there are more in the Norhern Hemisphere. First of all, deciduous forests are confined to regions with a temperate climate: that is, a C classification in the Köppen Climate classification. This climate is found in the parts of the southern hemisphere you describe: SE Australia, Rio de Janeiro region. Remember, most of the earth's land mass is on the northern hemisphere; together with the Cf-classification needed for temperate forests, suitable areas are limited. Here you can check the area where temperate forests would grow (if soil conditions are suitable). Not nearly as much as on the northern hemisphere. Another major problem is deforestation, as the Cf climate regions are often places for settlement and have huge urban areas (SW China, SE Australia, Rio de Janeiro region). You can see the impact on this map. Thus, limited landmass, little Cf-climate area and deforestation make for less temperate deciduous forests on the Southern Hemisphere. Pim Rijkee (talk) 22:13, 15 December 2009 (UTC)

I think the argument is valid, though limited landmass/climate area is probably a more major issue here. Jayron is right that most seasonal trees cannot survive the tropics "as they are", though it's obvious that there was a lot of exchange between hemispheres during the most recent ice age (i.e. subarctic varieties had moved so far south, and the tropics were probably so cool as to allow some of the northern varieties to travel to the south), and probably every cold period previously. Because of the large subarctic landmasses in the north, subarctic varieties of forest trees are more likely to produce successful genetic variations, and thus they will survive better in competition with other plants, preserving more species and higher populations. The southern subarctic varieties don't have as much suitable environment, so they come under more competition from non-subarctic varieties; that is as long as the gene pool isn't rejuvenated by transports from the north. 219.102.221.182 (talk) 06:20, 16 December 2009 (UTC)